1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier or printer of electrophotographic type or inkjet type, and in particular relates to reduction of the number of data signal lines.
2. Description of the Related Art
In for example a copier of the electrophotographic type, there may be provided various types of units that are capable of being detached from the main body of the apparatus and replaced. Various types of detection means are provided that detect the attached/detached state of these various replaceable units with respect to the main body of the apparatus and output a detection signal indicating this state. In addition, various types of actuators such as motors, solenoids or clutches are provided in the main body of the apparatus and these actuators are driven by means of drive means that are supplied with control signals from control means.
On the other hand, in addition to adaptation to color use, improved performance and multi-functionality are sought in the image forming apparatuses of recent years. This necessitates a large number of signal lines for transmission of for example detection signals from the various types of detection means, drive signals to the various types of actuators, and control signals from the control means, and the number of signal lines has tended to increase. Also, the various types of units, various types of detection means and actuators require power supply, so power supply lines and so forth are also necessary.
Consequently, due to the input and output to the control means of such a large number of signals through signal lines, the control means tends to become bulky. Furthermore, since the control means is installed in a location that is remote from the various types of units and various types of detection means, and a large number of signal lines are arranged running round the interior of the main body of the apparatus, these present a considerable obstacle to simplification, miniaturization and cost reduction of the apparatus.
In order to avoid such a large number of signal lines, in the image forming apparatus disclosed in Japanese Patent Application Laid-open No. 2002-258691, the signal lines that connect the image forming control means and the various units may be reduced in number by adopting an arrangement in which the various units are provided with an I/O expander and by the image forming control means identifying the various types of units according to the state of an input port of the I/O expander.
Also, in the image forming apparatus disclosed in Japanese Patent Application Laid-open No. 2006-218682, transfer data that is set when the transfer clock is at L level and loaded on the rise of the transfer clock is converted to image serial data and the rising edge signal of the transfer data when the transfer clock becomes H level is used as a control signal so that the image serial data and the control signal can be transferred by a common signal line.
With the image forming control means, when forming an image, it is necessary to carry out fine control of the drive means and actuators within the apparatus in accordance with the conditions at many locations in the apparatus and the operating state. In order to achieve such fine control of the drive means and actuators, even if the signal lines connecting the image forming control means and the various units are reduced in number by identifying the type of unit in accordance with the state of an input port of an I/O expander of the various units as disclosed in Japanese Patent Application Laid-open No. 2002-258691, or, as disclosed in Japanese Patent Application Laid-open No. 2006-218682, the image serial data and control signals are transferred by a common signal line, the number of signal lines that are input to the image forming control means and the number of signal lines that are output therefrom become enormous, resulting in complexity of the apparatus and making it difficult to miniaturize.
Also, when the system configuration of the image forming apparatus i.e. the number of input/output means thereof is altered, appropriate remodeling of the image forming control means (circuit board) and/or additional provision of connectors and so forth is necessary, resulting in increased costs.